The invention relates to an apparatus for and a method of recognizing unwanted material in a flow of fiber material in the textile industry, more particularly spinning plants. The invention further relates to a method and apparatus of recognizing unwanted material in a flow of fiber material in the textile industry, also known as a flow of material under measurement, in the form of an air-fiber mixture conveyed in a pneumatic conveying tube or in the form of a fleece, conveyed so as to be freely or mechanically movable. The invention covers the fields of sensor equipment, acoustics, optics, electronics and data processing. It is concerned with a method of and an apparatus for recognizing unwanted material in the form of string, woven fabrics, strips or foils in a flow of textile raw fiber material.
In the case of textile raw fibers such as raw cotton it is impossible to prevent unwanted material from getting into the raw material. The unwanted material may comprise pieces of metal, pieces of fabric, plastics, foils and tying materials such as strings, bands, threads or the like.
The separation of materials which, in their basic forms, have a structure and quality similar to those of the raw material, such as string material made of jute or synthetic fibers, is uncertain. Unless unwanted material of the latter kind is separated out in time, it goes right through the entire cleaning, carding and fiber-parallelizing processing, is mixed in with the fiber feed materials and is finally spun into yarn together with the wanted material. Because of the reduced tensile strength or poor adhesion between unwanted fibers and wanted fibers, yarn breakages occur during spinning or even as late as the weaving stage. The breakages lead to very undesirable downtimes of the spinning machinery and looms. Further problems occur in the dyeing of yarns or woven fabrics mixed with unwanted fibers since the wanted fibers and unwanted fibers may have different dyeing characteristics. This problem is very serious when the unwanted material is of plastics and the wanted material is a natural product such as cotton.